This invention relates to syringes and, more particularly, to a syringe where liquid trapped air in a filled syringe can be conveniently and readily expelled and to a method of using such a syringe.
One method for separating trapped air from a liquid contained in a filled syringe is described in U.S. Pat. No. 3,809,298. This patent discloses a syringe having a barrel with a bore communicating with a needle bore, the barrel bore having a distal enlarged portion where air trapped in a withdrawn liquid can escape from the liquid and remain in the enlarged portion while liquid is expelled from the syringe. It can be difficult to trap all air bubbles at the same time, especially if the air volume is greater than the enlargement. Also, when the liquid is expelled, no barrier prevents the air from returning to the liquid.
In U.S. Pat. No. 3,291,128, a hypodermic syringe is constructed with a barrel and annular ribs extending about a piston. The annular ribs must be elastic in order to provide for expulsion of trapped air from the barrel. However, if the ribs do not reform and immediately establish a sealing engagement with the barrel wall, leakage or discharge of syringe liquid can result.
In U.S. Pat. No. 2,263,865, either a spring operated knob or a sleeve cover are retracted to open an air hold and release liquid trapped air bubbles. When the knob or sleeve are released to allow air rejection, fluid can also be released to the outside of a syringe with messy and sometimes dangerous results. In addition, a sleeve cover can obliterate volume markings on a syringe. The present invention addresses the problems cited in prior art inventions by providing a reliable and simple means for air bubble release from liquids contained in syringes.
A primary objective of the present invention is to provide a sliding chamber means for removal of trapped air bubbles from syringe delivered liquids where a simple positive movement of the syringe plunger reliably releases small and large volumes of air without liquid spill.
Another objective of the invention is to provide a syringe where the user does not have to continuously tap the syringe and move a plunger back and forth to remove trapped air.
Still another objective is to provide a means for delivering an accurate volume of liquid to a user via syringe injection.
Finally, an objective of the present invention is to provide a sanitary and efficient means for syringe liquid trapped gas removal when a user has painful and/or weak fingers and is not able to vigorously snap or manipulate a syringe in order to remove gas bubbles.
The present invention provides an airless syringe with means for efficiently removing liquid trapped air bubbles so that accurate liquid volume measurements are possible comprising a cylindrical barrel with a sealed forward wall, the barrel defining a small opening at the barrel""s juncture with the sealed wall. The sealed wall exterior is provided with a centrally located tapered shank portion adapted to receive a conventional hypodermic needle inserted so as to be in communication with the barrel interior. The needle and the needle insertion means have no patentable significance relative to the invention herein. Within the barrel resides a plunger carrying a forward end piston. In order to provide a snug fit between the piston and barrel interior wall, the piston diameter is substantially equal in size to the barrel wall inside diameter. A positive movement of the plunger slides the piston smoothly back and forth inside the barrel.
An air release assembly located above the small barrel opening adjacent to the syringe front wall is slidingly mounted to the barrel exterior surface. The air release assembly is comprised of a barrel adjacent portion with means for smooth sliding on the barrel exterior surface and an upper chamber portion where trapped air is expelled. An opening extends through the sliding means portion and chamber portion for air transport from the barrel interior to an exterior environment. A mounting clamp slidingly clasps the air release assembly to the syringe barrel.
The airless syringe is filled with liquid when a user slides the air release assembly forward to a closed position, places the hollow needle below a liquid surface and pulls the plunger back to draw liquid into the syringe. Often air bubbles enter with the liquid. The airless syringe is titled so the needle is positioned upward causing trapped air to move to the area of the barrel opening. Now the user slides the air release assembly backward to an open position where the air release assembly opening is aligned with the barrel opening. Forward movement of the plunger pushes syringe trapped air through the barrel opening and the air release assembly opening into the upper portion chamber where trapped air is expelled. An absorbent material designed to receive syringe fluid accompanying expelled air resides in the chamber. Next, a simple forward movement of the air release assembly to a closed position prepares the syringe for use. By positive movement of the plunger, a user can safely inject a measured amount of liquid free of air bubbles.
The above prominent advantages and features of the present invention are further and more fully described by the following description which makes reference to the attached drawings.